In the cricket Telegryllus commodus, various brain lesions will be made or neck connectives severed and operated males will be exposed to various light, temperature and acoustic regimes to locate the timing-center and its afferent and efferent pathways for circadian singing-rhythms. Different regions of the pars intercerebralis will be coagulated in order to disrupt selectively each one of the three known rhythms: locomotion, stridulation and spermatophore formation. Dusk and dawn effects will be employed to determine the possible role of the ocelli in the entrainment process and sensory pathways for the entrainment of stridulation by temperature cycles will be sought. Tape-recorded songs of normal males will be tested for the reentrainment of arhythmically singing, bilobectomized males and of locomotor activity of females. White noise signals will also be employed to find out whether the clock can use unspecific information. Locomotion of all larval instarts will be continuously recorded to determine at what stage of growth the clock becomes operative. Studies of male:female encounters will be made to assess the role of the antennae in sex recognition and increased male-spermatophore production. Injections of testis-extracts into females will be used to test the hypothesis that a chemical factor is responsible for enhanced egg production and release following mating.